Utility of ctDNA to Manage Adjuvant Therapy in CRC Based on Results of the GALAXY Study - Episode 2

GALAXY Study Enrollment and Patient Cohorts

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Drs Cohen and Lewis review the GALAXY enrollment strategy and describe the various colorectal cancer patient cohorts in the study.

Transcript:

Mark Lewis, MD: Stacey, I am going to let you talk about this a bit, the consort diagram in the trial gets a little complicated in terms of how we end up analyzing patients in smaller populations. Would you mind walking our audience through what you see here?

Stacey A. Cohen, MD: Yes, thank you. As you mentioned, GALAXY is a very large study. They had over 1500 patients. In the study that was presented, they only included about 1000 patients, and they excluded some key groups that we might want to think about. Patients who went on an interventional trial that might conflict with the study were excluded, but also patients with a pathologic complete response, so those who you might expect to have very good outcomes were excluded from the study. And then [there were] patients who were missing various data points, whether from ctDNA [circulating tumor DNA] or pathologic specimen. Another key thing to know about the study is that this included a variety of different stages, but it did not mandate or follow what kind of neoadjuvant therapy patients may have received. That’s going to in some ways completely bias the results that we are getting because as we think about the role of adjuvant therapy, we all know that the benefit that might have been previously received in someone who had neoadjuvant therapy is very different than someone who just started with surgery. It’s a key thing to keep in mind, that this takes time zero, almost from the time of surgery, though some samples were collected in the preoperative setting.

Mark Lewis, MD: That’s so well said, that we think about who was taken out, and also in a minute we will talk about who is actually looked at in terms of dynamics, which are in the title of the abstract.

Stacey A. Cohen, MD: Exactly. So 188 patients were positive, with the key time point being that MRD [molecular residual disease] point of 4 weeks postoperatively, and that later funnels into the clearance analysis cohort of looking at how many patients could actually clear from ctDNA positive to negative. Also, 852 patients were ctDNA negative, and only a subset of those were actually included in the ctDNA negative cohort, again, because sometimes [patients had] very low-risk disease. So keep in mind there are a couple of time points where we have taken out maybe some of those best-outcome type patients. Separately from this, there was a dynamic cohort that Dr Lewis just referred to, and these are patients who not only have the 4-week time point but at minimum also have the 12-week time point, and of course we want to see beyond that. There are many different ways to slice and dice these data, but those are the 3 key cohorts that we are going to focus on: ctDNA positive at 4 weeks, ctDNA negative at 4 weeks, and those who had at least those first 2 samples.

Mark Lewis, MD: Thank you so much, Dr Cohen. I think it’s important, I kept coming back to the consort diagram as I was analyzing this abstract, and realized that [Masahito] Kotaka, [MD, PhD,] at the conference had a very limited amount of time to present a lot of very rich data. I think it’s really important as we go through these slides that we think about what group are we looking at here. One thing I wanted to point out about the dynamic analysis cohort, which got slightly condensed down to 838 patients, [is] if the patients recurred before that postoperative 12-week time point, they were removed from those dynamics. So again, I think you are saying that we have to be very discriminating in asking who are we studying right now in this subgroup analysis.

Transcript edited for clarity.